Human Immunodeficiency Virus Type 1 ("HIV-1") was identified as an etiological agent of Acquired Immune Deficiency Syndrome ("AIDS") in 1983 (Barre-Sinoussi et al., Science 220: 868-871, 1983) and 1984 (Gallo et al., Science 224: 500-503, 1984). Human Immunodeficiency Virus Type 2 ("HIV-2") was identified in 1986 and is an important cause of AIDS in Central and West Africa (Clavel et al., Science 233: 343-346, 1986) with some reported cases in Europe (Bruckner et al., Lancet i: 223, 1987; Saimot et al, Lancet i: 688, 1988) and the USA (New Jersey MMWR 87: 33-35, 1988).
The two retroviruses display rapid mutation (Hahn et al., Science 232: 1548-1553, 1986; Wen-Hsiung et al., Molec Biol Evol 5(4): 313-330, 1988; Saag et al., Nature 334: 440-444, 1988) and genetic polymorphism with more than 13 strains of HIV-1 and 4 strains of HIV-2 characterized by DNA sequencing (Myers et al., Human Retroviruses and AIDS, 1988. A compilation of nucleic acid and amino acid sequences. Los Alamos National Laboratory, Los Alamos, N. Mex. 87545, USA).
Tests for HIV infection currently licensed for use in the United States by the United States Food and Drug Administration ("USFDA") employ disrupted HIV-1 virus as the antigen (Petricciani et al., Ann Int Med 103: 726-729, 1985; Osterholm et al., New Engl J Med 312: 1185-1188, 1985) and are based upon the observation that HIV-1 proteins within these antigen preparations detect antibody as an indirect measure of infection (Allan et al., Science 228: 1091-1094, 1985; Barin et al., Science 228: 1094-1096, 1985; and Wain-Hopson et al., Cell 40: 9-17, 1985). These tests have been helpful in screening blood for HIV-1 contamination and diagnosing exposure to the AIDS virus, but remain limited in sensitivity when a single HIV-1 isolate is used as source of antigen (for example BH8 isolate, U.S. Pat. No. 4,520,113) since HIV displays rapid mutation and multiple genetic variants as noted above and antigenic variants exist (Looney et al., Science 241: 357-359, 1988; Palker et al., Proc Nat'l Acad Sci USA 85: 1932-1936, 1988). Insensitivity may also result from poor preservation of the immunodominant regions of the HIV gp41 envelope protein in current licensed assay kits that employ viral lysates as the antigen source (Steckelberg and Cockerill, Mayo Clinic Proc 63: 377-380, 1988). Further, since current kits employ only HIV-1 protein markers, it is estimated that 75% or more of HIV-2 infections will not be detected (Clavel et al., New Engl J Med 316: 1180-1185, 1987).
Tests for HIV infection based upon whole virus lysates as the antigen source have significant deficiencies with regard to specificity. The virus must be grown in cell cultures. HLA and other cell culture contaminants within the antigen may be responsible for false positivity (Eisenstaedt et al., Am J Public Health 78: 450-454, 1988; Goedest Ann Int Med 105: 609-610, 1988). In populations with a low prevalence of HIV infections, less than 1 in 10 persons who are repeatedly positive with the current tests may actually be infected with HIV (Osterholm et al., New Engl J Med 312: 1185-1188, 1985).
Related to the inadequate sensitivity and specificity of many current tests is the ability of a test to discriminate between positive and negative samples. Ward et al., JAMA 256: 357-361, 1986, found that over half of the positive results obtained with one test were just above the positive/negative cut-off value. An optimal test would show large differences between positives and negatives for nearly all samples, thereby decreasing the likelihood of false positive test results.
Subsequent refinements in HIV testing, not yet licensed by the USFDA for use within the United States, have employed HIV protein produced by recombinant DNA techniques (Thorn et al., J Clin Microbiol 25: 12070-1212, 1987; Burke et al., Ann Int Med 106: 671-676, 1987; Dawson et al., J Infect Dis 157: 149-157, 1988; and Beltz, et al., U.S. Pat. No. 4,753,873), synthetic peptides related to HIV proteins (Rosen et al., P.C.T. Application Publication No. WO87/06005; Wang et al., Proc Nat'l Acad Sci USA 86: 6159-6163, 1986; U.S. Pat. No. 4,735,896; Cosand, U.S. Pat. No. 4,629,783; Smith et al., J Clin Microbiol 25: 1498-1504, 1987; and Gnann et al., J Infect Dis 156: 261-267, 1987), or a combination of factors (Leslie et al., Vox Sang 54: 84-91, 1988). Nonspecificity due to tissue culture contaminants is obviated when either recombinant proteins or synthetic peptides are used as the antigen source, and neither antigen source requires exposure to HIV during the manufacturing process. Synthetic peptides additionally allow standardized antigen production by purely chemical means, and avoid nonspecificity resulting from contaminating proteins of Escherichia coli or other hosts employed to manufacture the HIV protein fragments produced by genetic engineering methods. New peptides may also be quickly incorporated into a manufacturing process if necessitated by mutations of HIV-1 or HIV-2 that affect antigenicity of peptides employed in the diagnostic test. These refinements produce improved tests for antibody to HIV-1, but significant difficulties remain with respect to further improvements in sensitivity and specificity, detection of HIV-2 infections, and adaption of these reagents to rapid simple assays for discrimination between positive and negative samples.